1. Field of Invention
This invention relates to the production and application of a device for use in papermaking machinery, and more importantly, the improved performance of the pulp fiber slurry relating to the molecular level bonding and liquid drainage of the paper product.
2. Description of Prior Art
A multitude of dewatering devices are known, yet, typically such devices are positioned across the width of the paper machine, underneath the continuous moving screen that the pulp slurry is delivered onto from the extruder or headbox. These units are of two schools: (1) roll configuration or (2) foil configuration. Both types of configurations provide (a) support of the continuous screen and (b) remove liquid, mainly water, from the pulp slurry. These devices traverse the width of the papermaking machine perpendicular to the machine sides or rails. The roll devices are attached to the rails typically, while the foil devices are normally attached to equipment referred to as boxes which are, also, usually attached to the rail. Attachment of the devices to the rail holds them securely in place as the continuous screen is moved across the top of the units which initiates liquid removal from the pulp slurry.
Both configurations of devices have distinct characteristics and advantages in the papermaking process. The roll configuration creates what is referred to as a "pulse" of liquid, as the screen is moved across the unit, vacuum is created on the back or downstream side of the roll pulling liquid through the screen from the slurry, the liquid coheses to the roll and as the roll turns, literally, pushes liquid back up into the slurry on the from or upstream side of the roll at the contact point of the screen. This disturbance or "pulse" creates activity in the slurry at the fiber level and under controlled conditions seems to help formation. Because of the size and surface area of the roll, "pulse" is difficult to control and drainage of the liquid is adequate at best, especially, at higher machine speeds.
The foil configuration exhibits more efficient drainage characteristics than the roll configuration but slurry activity is diminished because less "pulse" is available. Current foil designs allow faster screen speeds over shorter distances because of increased drainage capabilities but formation or fiber bonding then becomes the issue.
The deficiencies of the current designs are: (1) cross direction fiber movement crucial to the optimal fiber bonding is inhibited as the liquid is removed, the fibers are forced down in straight lines. Poor formation is enhanced by current straight line drainage devices and techniques which often lead to streaking and marking and overall lower quality of the pulp product; (2) the continuous screen is supported on narrow points, the contact point of a roll or the nose portion of a foil; (3) often because of the straight line liquid removal, entire machine tables are moved back and forth or oscillated in an attempt to regain cross direction fiber movement and improve poor sheet formation. This movement is a massive undertaking. Because of the size of the equipment that is moved back and forth this motion is severely limited in speed and effectiveness. Often the entire sheet only realizes a tiny fraction of the overall movement of one or two inches; (4) Presently, the devices available are of one design or the other and provide only those characteristics that type employs and adjustment requires complete change to another device.